How about repetitive gusts and possible resonance? But remember the Sam
Harris / W1FZ philosophy - "If it stays up more than two winters it was over
designed".
----- Original Message -----
From: "Jim Thomson" <Jim.thom@telus.net>
To: <towertalk@contesting.com>
Sent: Wednesday, January 27, 2010 10:09 AM
Subject: [TowerTalk] sched 80 mast
> VE9HF indicates his sched 80 mast is .25" thick. It's not.
>
> IF his mast is typ 1.9" OD sched 80 stuff... it's only .200" thick.
> His section modulus is only .412
>
> If the yield strength is 35 ksi.... his max bending moment is only
> .412 x 35 ksi = 14,420 in lbs...[ 1200 ft lbs]
>
> Lets say 7 sq feet @ 70 mph [20 lbs per sq ft] x 14' .... = 1960
> ft lbs of bending moment.
>
> 1960> 1200 ! The mast will snap like a tooth pick. The mast is
> maxed out with 1200/140 = 8.57'
>
> This doesn't even factor in the other TWO proposed yagi's... nor the
> wind load of the mast itself !
>
> It's NOT....." a serious tower" . It's made for TV ants'... and
> can be used with ham ant's,
>
> provided you don't overload it...esp with tall masts. Even if you guyed
> the tower, the proposed mast you
>
> are contemplating will fold over at a right angle. That Delhi isn't
> CSA approved, nor does it meet
>
> the Canadian S-37 tower specs. Load it up with heavy wet snow + a tiny
> bit of ice .....+ a 55 mph gust
>
> .. and it's bye-bye tower... plus 3 x ants' trashed. Removing a bent
> mast is a gong show in itself.. and
>
> extremely dangerous. If you want a stronger, self support tower, get
> a Trylon Titan..[with the 48" wide bottom section]...
>
> ... or better yet ..a Trylon Super Titan. The Trylon super Titan IS a
> S-37 rated tower, and will handle 25 mm of radial ice + high wind.
>
> It's the real deal. The stock Delhi top bearing plate + mating thrust
> bearing is pure junk. The rotor plate is worse. You will end up
>
> tearing up all the plates within months.
>
> Later.......... Jim VE7RF
>
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